With a focus on fuel economy and increasing system pressures to achieve greater levels of machine performance, there is a trend for more hydraulic or fluid systems to utilize a variable displacement pump. The variable displacement pump is more efficient, and its abilities to “destroke”, i.e., operating at reduced displacement and/or pressure levels, can reduce fuel consumption. In an attempt to maximize efficiency, most variable displacement pumps operate in a closed center mode, in which generally, the system provides maximum fluid pressure to the control valves of the system, irrespective of whether the valves are actuated or not. The pumps vary their flow rate, pumping significantly reduced amounts of pressurized fluid until an operator actuates a valve associated with a hydraulic actuator controlling an attachment, such as associated with operation of a work vehicle, for example, a backhoe or backhoe loader. A benefit of a closed center system is that a hydraulic pump is destroked at stall and also at standby conditions, only supplying a required flow of pressurized fluid upon demand, which reduces losses associated with system operation. However, operating in a closed center mode increases the complexity of the system, resulting in increased operating costs.
Variable displacement pumps can also be used in an open center operating mode, in which the pump provides a continuous flow of pressurized fluid to the system. While systems utilizing a conventional open center operating mode are less complex and therefore less expensive to operate his compared to operating in a closed center mode, there are drawbacks associated with a conventional open center operating mode. For example, in a standby condition, the pump operates at a maximum displacement condition, resulting in lower operating efficiencies.
Accordingly, it would be desirable to inexpensively operate a pump in an open center mode that would permit the pump to operate at a destroked or minimized displacement condition in response to the system operating in either a standby mode or a stall mode.